Natural oils/fats, mixtures of natural oils/fats, hydrogenated oils and transesterified oils thereof are mixtures of various triglycerides having different melting points. An oil/fat is used for wide range of applications such as frying oil/fat, margarine/shortening oil/fat, filling oil/fat, and chocolate oil/fat, and the like depending on physical properties thereof. Separation of oil/fat such as dry-mode oil/fat separation and solvent separation has been widely put into practical use as one of the processing techniques for adjusting physical properties of oils/fats.
The above-mentioned solvent separation has been suitably used since early times for fractionation of a crystal fraction and a liquid fraction, but a large amount of hexane or acetone, which is an organic solvent, is required. Accordingly, in recent years, a dry-mode oil/fat separation method which is simpler and safer has been extensively studied from the viewpoint of safety and security.
A dry-mode oil/fat separation method is a method in which, in general, a raw material oil/fat completely melted by heating without using a solvent is cooled in a crystallization tank while stirring to precipitate (crystallize) a crystal, and then the precipitate is fractionated into a crystal fraction and a filtrate (unsolidified low-melting-point fraction) by compression and filtration. The method has already been widely used for separating palm kernel oil, butter oil, and palm oil.
The dry-mode oil/fat separation method is more preferable than solvent separation also in terms of energy efficiency. However, there are problems such as solid-liquid separability between a crystal fraction and a liquid fraction is low when compared with solvent separation, removing a liquid fraction entrapped by a crystal fraction is not easy, and when an amount of crystals after crystallization is too large, a viscosity of a crystal slurry increases, and therefore separation by compression and filtration becomes difficult to perform.